The International Civil Aviation Organization (ICAO) defines a runway incursion as “Any occurrence at an aerodrome involving the incorrect presence of an aircraft, vehicle, or person on the protected area of a surface designated for the landing and take-off of aircraft.” The U.S. Federal Aviation Administration (FAA) adopted the ICAO definition in October 2007. Runway incursions obviously create the risk that an airplane taking off or landing will collide with whatever object is on the runway. The Mar. 27, 1977 Tenerife airport disaster, in which 583 people were killed in the deadliest aviation accident in history, began with a runway incursion.
Airport surface monitoring began with simple visual monitoring by air traffic controllers. Later systems invoked surface radar and multilateration. Surface radar and multilateration systems address a significant component of the ground control requirements; however, neither system alone provides a comprehensive solution as limitations exist with each system. In the case of surface radar, blind spots, multipathing, antenna period, and clutter tend to affect the usability of the system. In the case of multilateration (MLAT), targets without an active transponder will not be detected or tracked by the system. Some pilots off their transponders after landing or aircraft automatically disable the transponder on the ground, which renders them invisible to the MLAT system. Furthermore, most airport vehicles do not have transponders. Accordingly, the information presented to the air traffic personnel can be incomplete or inaccurate, thereby leading to potential safety issues since a properly tracked vehicle or aircraft could be directed to an area where an undetected aircraft may be residing.
Following the Tenerife disaster, aviation authorities looked past surface search radars to find systems and implement procedures and to better improve runway safety by limiting runway incursions. For example, in the U.S., systems such as Airport Surface Detection Equipment—Model X (ASDE-X) and Airport Surface Surveillance Capability (ASSC) have improved airport surface safety and efficiency with surveillance and safety alerts for air traffic control (ATC), but these systems are installed only at the largest U.S. airports. ASDE-X is deployed at 35 airports and ASSC will be deployed at 9 additional. Installation of these systems at additional airports is not currently planned. In contrast to air traffic controller alerting systems, the FAA's Runway Status Lights (RWSL) system addresses runway safety by directly providing aircraft and ground vehicles with improved situational awareness. RWSL uses automatically controlled in-pavement lights to signal the pilot if it is unsafe to enter the runway. RWSL is a fully automatic, advisory safety system designed to reduce the number and severity of runway incursions and prevent runway accidents while not interfering with airport operations. RWSL is designed to be compatible with existing procedures and to operate without adding to air traffic controller workload. RWSL uses surveillance sources (such as ASDE-X or ASSC), light control logic, and a Field Lighting Subsystem (FLS) with arrays of in-pavement light fixtures. The FLS provides RWSL with two types of lights: Runway Entrance Lights (REL) and Takeoff Hold Lights (THL). Normally, the REL and THL lights are extinguished. REL illuminate red when it is unsafe to enter the runway. THL lights illuminate red when it is unsafe to begin departure. A pilot still requires a clearance from the controller to enter or cross a runway or begin a departure. Thus, RWSL provides an additional, independent layer of safety, but use of FLS adds greatly to the cost and complexity of RWSL. For example, a typical FLS may involve multiple power shelters, constant current airfield lighting circuits, and several hundred in-pavement light locations-each with fixture, addressable controller, and power transformer components installed. Maintenance is a significant expense over the lifecycle of the system due to the harsh airport runway environment's effect on the FLS equipment. The RWSL program only includes 17 major airports (15 are currently operational). As reported in FAA Operational and Programmatic Deficiencies Impede Integration of Runway Safety Technologies”, Office of the Inspector General (OIG) Audit Report, AV-2014-060, Jun. 26, 2014, Page 2, available at https://www.oig.dot.gov/sites/default/files/FAA%20Surface%20Surveillance%20Technolologies%5E6-26-14.pdf, technical problems and unexpected costs related to the construction and operation of the in-pavement FLS delayed implementation significantly and contributed to the decision to remove six airports from the original implementation plan. This leaves hundreds of other airports without the safety benefits of RWSL. A way to provide the RWSL safety benefits to pilots without relying on costly FLS and related infrastructure is needed.
One current or soon to be implemented system that may be leveraged to assist in runway incursion prevention is the Automatic Dependent Surveillance-Broadcast system (ADS-B). ADS-B is the foundation of the FAA's Next General Air Transportation System (NextGen), a satellite-based system that was implemented to make the nation's airspace more efficient. There are two types of ADS-B service that may be implemented on an airplane: ADS-B Out and ADS-B In. Both are valuable, but as of 2015, only ADS-B Out is mandated by the FAA's Final Rule, which states that all aircraft operating in designated airspace must be equipped with ADS-B Out by Jan. 1, 2020. ADS-B will allow air traffic controllers and other participating aircraft to receive extremely accurate information about an aircraft's location and flight path, which, in turn will allow for safer operations, reduced separation standards between aircraft, more direct flight routes and cost savings for operators. ADS-B Out is the “broadcast” part of ADS-B. An aircraft equipped with ADS-B Out capability will continuously transmit aircraft data, such as airspeed, altitude and location, to other aircraft with ADS-B In service and to ADS-B ground stations. ADS-B ground stations provide additional information in their ADS-B broadcasts, possibly including the position reports of non-ADS-B Out equipped aircraft if they are detected by other FAA cooperative (secondary surveillance radar (SSR) and FAA non-cooperative surveillance systems (e.g., radar-based). The minimum equipment needed for ADS-B Out capability includes an ADS-B-approved transmitter—either a 1090 MHz Mode S transponder or a dedicated 978 MHz UAT for use with a previously installed Mode C or Mode S transponder—and a WAAS-enabled GPS system. ADS-B In is the receiver part of the system. ADS-B In equipment allows aircraft, when equipped properly, to receive and interpret other participating aircraft's ADS-B Out data on a computer screen or an Electronic Flight Bag in the cockpit.
An electronic flight bag (EFB) is an electronic information management device that helps flight crews perform flight management tasks more easily and efficiently with less paper. An EFB is a general-purpose computing platform intended to reduce, or replace, paper-based reference material often found in the pilot's carry-on flight bag, including the aircraft operating manual, flight-crew operating manual, and navigational charts (including moving map for air and ground operations).